Opposing effects of two osmolytes ? trehalose and glycerol ? on thermal inactivation of rabbit muscle 6-phosphofructo-1-kinase

Kramers’ Theory and the Dependence of Enzyme Dynamics on Trehalose-Mediated Viscosity

The disaccharide trehalose is accumulated in the cytoplasm of some organisms in response to harsh environmental conditions. Trehalose biosynthesis and accumulation are important for the survival of such organisms by protecting the structure and function of proteins and membranes. Trehalose affects the dynamics of proteins and water molecules in the bulk and the protein hydration shell. Enzyme catalysis and other processes dependent on protein dynamics are affected by the viscosity generated by trehalose, as described by the Kramers’ theory of rate reactions. Enzyme/protein stabilization by trehalose against thermal inactivation/unfolding is also explained by the viscosity mediated hindering of the thermally generated structural dynamics, as described by Kramers’ theory. The analysis of the relationship of viscosity–protein dynamics, and its effects on enzyme/protein function and other processes (thermal inactivation and unfolding/folding), is the focus of the present work regarding the disaccharide trehalose as the viscosity generating solute. Finally, trehalose is widely used (alone or in combination with other compounds) in the stabilization of enzymes in the laboratory and in biotechnological applications; hence, considering the effect of viscosity on catalysis and stability of enzymes may help to improve the results of trehalose in its diverse uses/applications.

Changing relations between proteins and osmolytes: a choice of nature

The stabilization and destabilization of the protein in the presence of any additive is mainly attributed to its preferential exclusion from protein surface and its preferential binding to the protein surface, respectively.

Quantifying the molecular origins of opposite solvent effects on protein-protein interactions

Although the nature of solvent-protein interactions is generally weak and non-specific, addition of cosolvents such as denaturants and osmolytes strengthens protein-protein interactions for some proteins, whereas it weakens protein-protein interactions for others. This is exemplified by the puzzling observation that addition of glycerol oppositely affects the association constants of two antibodies, D1.3 and D44.1, with lysozyme. To resolve this conundrum, we develop a methodology based on the thermodynamic principles of preferential interaction theory and the quantitative characterization of local protein solvation from molecular dynamics simulations. We find that changes of preferential solvent interactions at the protein-protein interface quantitatively account for the opposite effects of glycerol on the antibody-antigen association constants. Detailed characterization of local protein solvation in the free and associated protein states reveals how opposite solvent effects on protein-protein interactions depend on the extent of dewetting of the protein-protein contact region and on structural changes that alter cooperative solvent-protein interactions at the periphery of the protein-protein interface. These results demonstrate the direct relationship between macroscopic solvent effects on protein-protein interactions and atom-scale solvent-protein interactions, and establish a general methodology for predicting and understanding solvent effects on protein-protein interactions in diverse biological environments.

Characterization of the proteostasis roles of glycerol accumulation, protein degradation and protein synthesis during osmotic stress in C. elegans

Exposure of C. elegans to hypertonic stress-induced water loss causes rapid and widespread cellular protein damage. Survival in hypertonic environments depends critically on the ability of worm cells to detect and degrade misfolded and aggregated proteins. Acclimation of C. elegans to mild hypertonic stress suppresses protein damage and increases survival under more extreme hypertonic conditions. Suppression of protein damage in acclimated worms could be due to 1) accumulation of the chemical chaperone glycerol, 2) upregulation of protein degradation activity, and/or 3) increases in molecular chaperoning capacity of the cell. Glycerol and other chemical chaperones are widely thought to protect proteins from hypertonicity-induced damage. However, protein damage is unaffected by gene mutations that inhibit glycerol accumulation or that cause dramatic constitutive elevation of glycerol levels. Pharmacological or RNAi inhibition of proteasome and lyosome function and measurements of cellular protein degradation activity demonstrated that upregulation of protein degradation mechanisms plays no role in acclimation. Thus, changes in molecular chaperone capacity must be responsible for suppressing protein damage in acclimated worms. Transcriptional changes in chaperone expression have not been detected in C. elegans exposed to hypertonic stress. However, acclimation to mild hypertonicity inhibits protein synthesis 50–70%, which is expected to increase chaperone availability for coping with damage to existing proteins. Consistent with this idea, we found that RNAi silencing of essential translational components or acute exposure to cycloheximide results in a 50–80% suppression of hypertonicity-induced aggregation of polyglutamine-YFP (Q35::YFP). Dietary changes that increase protein production also increase Q35::YFP aggregation 70–180%. Our results demonstrate directly for the first time that inhibition of protein translation protects extant proteins from damage brought about by an environmental stressor, demonstrate important differences in aging- versus stress-induced protein damage, and challenge the widely held view that chemical chaperones are accumulated during hypertonic stress to protect protein structure/function.

Muscle-type 6-phosphofructo-1-kinase and aldolase associate conferring catalytic advantages for both enzymes

6-Phosphofructo-1-kinase (PFK) and aldolase are two sequential glycolytic enzymes that associate forming heterotetramers containing a dimer of each enzyme. Although free PFK dimers present a negligible activity, once associated to aldolase these dimers are as active as the fully active tetrameric conformation of the enzyme. Here we show that aldolase-associated PFK dimers are not inhibited by clotrimazole, an antifungal azole derivative proposed as an antineoplastic drug due to its inhibitory effects on PFK. In the presence of aldolase, PFK is not modulated by its allosteric activators, ADP and fructose-2,6-bisphosphate, but is still inhibited by citrate and lactate. The association between the two enzymes also results on the twofold stimulation of aldolase maximal velocity and affinity for its substrate. These results suggest that the association between PFK and aldolase confers catalytic advantage for both enzymes and may contribute to the channeling of the glycolytic metabolism.

Interactions of formulation excipients with proteins in solution and in the dried state

A variety of excipients are used to stabilize proteins, suppress protein aggregation, reduce surface adsorption, or to simply provide physiological osmolality. The stabilizers encompass a wide variety of molecules including sugars, salts, polymers, surfactants, and amino acids, in particular arginine. The effects of these excipients on protein stability in solution are mainly caused by their interaction with the protein and the container surface, and most importantly with water. Some excipients stabilize proteins in solution by direct binding, while others use a number of fundamentally different mechanisms that involve indirect interactions. In the dry state, any effects that the excipients confer to proteins through their interactions with water are irrelevant, as water is no longer present. Rather, the excipients stabilize proteins through direct binding and their effects on the physical properties of the dried powder. This review will describe a number of mechanisms by which the excipients interact with proteins in solution and with various interfaces, and their effects on the physical properties of the dried protein structure, and explain how the various interaction forces are related to their observed effects on protein stability.

Regulation of mammalian muscle type 6-phosphofructo-1-kinase and its implication for the control of the metabolism

Phosphofructokinase (PFK) is a major regulatory glycolytic enzyme and is considered to be the pacemaker of glycolysis. This enzyme presents a puzzling regulatory mechanism that is modulated by a large variety of metabolites, drugs, and intracellular proteins. To date, the mammalian enzyme structure has not yet been resolved. However, it is known that PFK undergoes an intricate oligomerization process, shifting among monomers, dimers, tetramers, and more complex oligomeric structures. The equilibrium between PFK dimers and tetramers is directly correlated with the enzyme regulation, because the dimer exhibits very low catalytic activity, whereas the tetramer is fully active. Several PFK ligands modulate the enzyme, favoring the formation of its dimers or tetramers. The present review integrates recent findings regarding the regulatory aspects of muscle type PFK and discusses their relation to the control of metabolism.

Kinetics of the thermal inactivation and aggregate formation of rabbit muscle pyruvate kinase in the presence of trehalose

In a previous study we found that 30-40% dimethylsulfoxide induces the active conformation of rabbit muscle pyruvate kinase. Because dimethylsulfoxide is known to perturb structure and function of many proteins, we have explored the effect of trehalose on the kinetics of thermal inactivation and stability of pyruvate kinase; this is because trehalose, in contrast to dimethyl sulfoxide, is totally excluded from the hydration shell of proteins. The results show that 600 mM trehalose inhibits the activity of pyruvate kinase by about 20% at 25 degrees C, however, trehalose protects pyruvate kinase from thermal inactivation at 60 degrees C, increases the Tm(app) of unfolding by 7.2 degrees C, induces a more compact state, and stabilizes its tetrameric structure. The inactivation process is irreversible due to the formation of protein aggregates. Trehalose diminishes the rate of formation of intermediates with propensity to aggregate, but does not affect the extent of aggregation. Remarkably, trehalose affects the aggregation process by inducing aggregates with amyloid-like characteristics.

Calmodulin upregulates skeletal muscle 6-phosphofructo-1-kinase reversing the inhibitory effects of allosteric modulators

6-phosphofructo-1-kinase (PFK) is a calmodulin (CaM)-binding protein that plays a key role on the regulation of glycolysis. Each PFK monomer binds two CaM molecules inducing the dissociation of the active tetrameric conformation of the enzyme into dimers, thus inhibiting it. Recently, we have reported that the binding of one CaM per PFK monomer promotes the dimerization of the enzyme although maintaining its full catalytic activity. The present work aims to understand the regulatory role of these active PFK dimers induced by CaM. We show that the inhibition of PFK activity by ATP (>1 mM) is abolished in the presence of CaM. CaM decreases the affinity of PFK for its substrates, fructose-6-phophate and ATP. Moreover, CaM activates PFK in the presence of citrate and lactate, two inhibitory metabolites that induce the dimerization of PFK tetramers, as well as potentiate the stimulatory action of ADP and fructose-2,6-bisphosphate. Under all the conditions tested CaM induces the formation of PFK dimers, supporting that these CaM-bound dimers are active and less susceptible to inhibition by allosteric ligands. In the end, we suggest that CaM binding to PFK, which is stimulated by Ca(2+), represents an important way to increase the glycolytic pathway in cells.

ATP and fructose-2,6-bisphosphate regulate skeletal muscle 6-phosphofructo-1-kinase by altering its quaternary structure

Recently, it has been demonstrated that fructose-2,6-bisphosphate (F2,6BP) protects skeletal muscle 6-phosphofructo-1-kinase (PFK) from thermal inactivation (50 degrees C) and against the deleterious effects of guanidinium hydrochloride (GdmCl). On the other hand, ATP, when added at its inhibitory concentrations, that is, >1 mM, enhanced either the thermal- or GdmCl-induced inactivation of PFK. Moreover, we concluded that these phenomena were probably due to the stabilization of PFK tetrameric structure by F2,6BP, and the dissociation of this structure into dimers induced by ATP. Aimed at elucidating the effects of F2,6BP and ATP on PFK at the structural and functional levels, the present work correlates the effects of these metabolites on the equilibrium between PFK dimers and tetramers to the regulation promoted on the enzyme catalytic activity. We show that ATP present a dual effect on PFK structure, favoring the formation of tetramer at stimulatory concentrations (up to 1 mM), and dissociating tetramers into dimers at inhibitory concentrations (>1 mM). Furthermore, F2,6BP counteracted this later ATP effect at either the structural or catalytic levels. Additionally, the effects of both F2,6BP or ATP on the equilibrium between PFK tetramers and dimers and on the enzyme activity presented a striking parallelism. Therefore, we concluded that modulation of PFK activity by ATP and F2,6BP is due to the effects of these ligands on PFK quaternary structure, altering the oligomeric equilibrium between PFK tetramers and dimers.

Fructose-2,6-bisphosphate counteracts guanidinium chloride-, thermal-, and ATP-induced dissociation of skeletal muscle key glycolytic enzyme 6-phosphofructo-1-kinase: A structural mechanism for PFK allosteric regulation

Rabbit muscle 6-phosphofructo-1-kinase (PFK) is the key glycolytic enzyme being regulated by diverse molecules and signals. This enzyme may undergo a reversible dissociation from a fully active homotetramer to a quite inactive dimer. There are evidences that some positive and negative modulators of PFK, such as ADP and citrate, may interfere with the enzyme oligomeric structure shifting the tetramer-dimer equilibrium towards opposite orientations, where the negative modulators favor the dissociation of tetramers into dimers and vice versa. PFK is allosterically inhibited by ATP at its physiological range of concentration, an effect counteracted by fructose-2,6-bisphosphate (F2,6BP). However, the structural molecular mechanism by which ATP and F2,6BP regulate PFK is hitherto demonstrated. The present paper aimed at demonstrating that either the ATP-induced inhibition of PFK and the reversion of this inhibition by F2,6BP occur through the same molecular mechanism, i.e., the displacement of the oligomeric equilibrium of the enzyme. This conclusion is arrived assessing the effects of ATP and F2,6BP on PFK inactivation through two distinct ways to dissociate the enzyme: (a) upon incubation at 50 degrees C, or (b) incubating the enzyme with guanidinium hydrochloride (GdmCl). Our results reveal that temperature- and GdmCl-induced inactivation of PFK prove remarkably more effective in the presence 5mM ATP than in the absence of additives. On the other hand, the presence of 100 nM F2,6BP attenuate the effects of both high-temperature exposition and GdmCl on PFK, even in the simultaneous presence of 5mM ATP. These data support the hypothesis that ATP shifts the oligomeric equilibrium of PFK towards the smaller conformations, while F2,6BP acts in the opposite direction. This conclusion leads to important information about the molecular mechanism by which PFK is regulated by these modulators.

Stabilization of yeast hexokinase A by polyol osmolytes: Correlation with the physicochemical properties of aqueous solutions

Osmolytes of the polyol series are known to accumulate in biological systems under stress and stabilize the structures of a wide variety of proteins. While increased surface tension of aqueous solutions has been considered an important factor in protein stabilization effect, glycerol is an exception, lowering the surface tension of water. To clarify this anomalous effect, the effect of a series of polyols on the thermal stability of a highly thermolabile two domain protein yeast hexokinase A has been investigated by differential scanning calorimetry and by monitoring loss in the biological activity of the enzyme as a function of time. A larger increase in the T(m) of domain 1 compared with that of domain 2, varying linearly with the number of hydroxyl groups in polyols, has been observed, sorbitol being the best stabilizer against both thermal as well as urea denaturation. Polyols help retain the activity of the enzyme considerably and a good correlation of the increase in T(m) (DeltaT(m)) and the retention of activity with the increase in the surface tension of polyol solutions, except glycerol, which breaks this trend, has been observed. However, the DeltaT(m) values show a linear correlation with apparent molal heat capacity and volume of aqueous polyol solutions including glycerol. These results suggest that while bulk solution properties contribute significantly to protein stabilization, interfacial properties are not always a good indicator of the stabilizing effect. A subtle balance of various weak binding and exclusion effects of the osmolytes mediated by water further regulates the stabilizing effect. Understanding these aspects is critical in the rational design of stable protein formulations.

Trehalose and glycerol stabilize and renature yeast inorganic pyrophosphatase inactivated by very high temperatures

A number of naturally occurring small organic molecules, primarily involved in maintaining osmotic pressure in the cell, display chaperone-like activity, stabilizing the native conformation of proteins, and protecting them from various kinds of stress. Most of them are sugars, polyols, amino acids or methylamines. Similar to molecular chaperones, most of these compounds have no substrate specificity, but some specifically stabilize certain proteins. In the present work, the capacity of trehalose and glycerol, two well-known osmolytes, to stabilize and renature inorganic pyrophosphatase is demonstrated. Both trehalose and glycerol significantly protect pyrophosphatase against thermoinactivation achieved by incubating the enzyme at temperatures up to 95 degrees C, and allow the enzyme already inactivated in the presence of these osmolytes to renature upon incubation at low temperatures. To the best of our knowledge, there are no data on the effects of these compounds on renaturation of thermoinactivated proteins. The correlation between the recovery of enzyme activity and structural changes indicated by fluorescence spectroscopy contribute to better understanding of the protein stabilization mechanism.